FIG. 1A illustrates a prior art computer system 100 including a host processor 116, a host adapter device 110 and a peripheral device 130, e.g. a disk drive. Host processor 116 and host adapter device 110 are connected to each other by a system bus 120. Host adapter device 110 includes a local microprocessor 111 connected to a local bus 115. Most adapter device 110 also includes a host adapter integrated circuit 112 that transfers data between local bus 115 and system bus 120, between local bus 115 and I/O bus 114, and between system bus 120 and I/O bus 114.
In computer system 100, the status of use of I/O bus 114 is indicated by a light emitting diode (LED) 113 in host adapter device 110. LED 113 may be mounted physically adjacent peripheral device 130 and indicates to a user that host adapter device 110 is accessing peripheral device 130. Local microprocessor 111 drives a signal to turn on LED 113 whenever local microprocessor 111 issues a command to access peripheral device 130. Subsequently, when the issued command is completed, local microprocessor 111 drives a signal to turn off LED 113. Therefore, LED 113 does not indicate use of I/O bus 114 in real time.
FIG. 1B illustrates another computer system 150, similar to computer system 100 of FIG. 1A except for host adapter device 140. Host adapter device 140 includes a local microprocessor 141 and two host adapter integrated circuits 143 and 142 all connected to local bus 145. Host adapter integrated circuits 142 and 143 have LEDs 142L and 143L respectively, each LED connected to the busy signal line BSY of I/O bus 114. LEDs 142L and 143L indicate usage of I/O bus 114 in real time. However, both LEDs 142L and 143L are turned on simultaneously by any activity that causes an active signal on the busy signal line BSY of I/O bus 114. For instance, when only host adapter integrated circuit 142 is used by local microprocessor 141 to communicate with peripheral device 130, both LEDs 142L and 143L are turned on because both LEDs are tied to the same busy signal line BSY.